This script causes major lag for some reason, any help?

So, I have a script like this:

function changed(Size)
    local a = script.Parent.Parent.Size -- script.Parent.Parent is a part
    local pos = script.Parent.Parent.position.Value -- script.Parent.Parent.position is a NumberValue
    local value = script.Parent.Parent.Value.Value -- script.Parent.Parent.Value is a Vector3Value
    local x, y, z = value.x, value.y, value.z
    value = Vector3.new(x, (pos), z)
    script.Parent.Parent.CFrame = CFrame.new(value)
end

script.Parent.Parent.Changed:connect(changed)

So, whenever I clone an object that has this script in it, the game just freezes for 5 seconds, but I have no idea why. This script is just supposed to lower a block by a certain number of studs on the y coordinate as the position value changes. When the lag clears, the script itself works fine.